The invention relates to a device on a motor vehicle with a brake and brake operating element, a drive assembly with a drive power source and an automatic transmission, a power control element for the drive power source, and a selector lever mechanism for shifting the automatic transmission only after the brake has been operated. A locking mechanism is integrated with the throttle to disable the power delivery system unless the brake has been operated.
In motor vehicles with automatic transmissions and without clutch pedals, inexperienced persons in particular or ones familiar with a vehicle having a gearshift mechanism and clutch pedal experience the disconcerting sensation of slow or abrupt forward or rearward movement of the vehicle immediately after a speed range is entered. This phenomenon is observed especially in motor vehicles having hydrodynamic torque converters between the internal combustion engine and transmission and also when the idling speed has been set too high or the hot running speed is high. If a speed range is entered when space is cramped (as, for example in a garage or with the vehicle parked between two other vehicles) and the operator fails to pay full attention, he is surprised by the abrupt, unexpected starting of the vehicle and may find himself in a stress situation in which wrong action may be taken. Hence the operating instructions of such vehicles recommend that the operating brake of the vehicle (foot brake) be applied before a speed range is engaged.
In addition, DE-OS (German Patent Disclosure) No. 32 38 196 discloses a device in which an actuator for the braking system of a vehicle is operated automatically if the speed of travel is below a boundary value near zero and if the brake pedal and accelerator pedal have not been operated. The automatic braking is cancelled when the accelerator pedal and/or brake pedal is operated. Aside from the high engineering cost involved in intervention (automatic braking) in the braking system of the vehicle, the situation described in the foregoing may not be eliminated, inasmuch as the vehicle nevertheless starts out abruptly when the accelerator pedal is operated, because of the automatic release of the brake.
The object of the invention is to employ relatively simple means to avoid a stress situation or abrupt starting of a vehicle when a gear speed range is entered from the neutral position of the transmission, without action by the operator.
Features of the invention are described herein often overcome many of the deficiencies noted above. In the invention, means that act directly on the drive power source or on the power control element, such as the accelerator pedal or its linkage, are connected to the brake operating system and the selector mechanism. These means are so designed that, when a gear speed is engaged from the neutral position or the park position of the transmission, the power output of the internal combustion engine is disabled if the brake of the vehicle has not been applied. Disabling the power output means that the internal combustion engine is either switched off or its idling speed position blocked. As soon as the brake of the vehicle, and the foot brake in particular, has been applied, the means are deactivated and the vehicle may be put in gear or accelerated. As a result of this measure the operator is forced to apply the brake before the vehicle starts out, so that uncontrolled starting is precluded. Provided that the starting torque or creep speed torque is high enough, the vehicle can now be driven or maneuvered, if necessary with an accuracy of centimeters, by varying the brake pressure with the brake actuating element or brake pedal. Only if the available creep speed torque is not high enough does the operator shift his foot from the brake pedal to the accelerator pedal.
The means for disabling the power output may comprise either a valve for interrupting the delivery of fuel, an interlock device blocking the power control element in a suitable position, or, in the case of a throttle-controlled internal combustion engine as drive power source, a second throttle valve in the intake manifold. The latter option is of interest especially if the vehicle already has a second throttle valve as a component of a drive slip regulation system. The effect claimed for the invention can be achieved in this case without great additional expense by providing a suitable logical switching circuit in the control electronics of the drive slip regulation system.
On engagement of a gear speed from the neutral position of the automatic transmission, in particular, it may be advantageous for the means of disabling the power output of the drive power source also to be deactivatable by the hand brake. If desired, both brakes (foot brake and hand brake) may be included in the control system claimed for the invention, so that the vehicle is braked each time that a gear speed is engaged.
In another embodiment, a speed detection system is employed to disable the power source at a preselected vehicle speed. This insures that, with the vehicle in motion and in the event of any unintentional shifting of the selector mechanism into the neutral position followed by reshifting into a forward drive position, there is no need for braking first to permit immediate power output from the internal combustion engine or immediate reacceleration.
In addition, an engine speed detection mechanism may be provided to deactivate the means for disabling the power output at a low speed of the drive power source at which creep speed torque is hardly to be expected, independently of operation of the brake, or, if the speed of the drive power source is too high, as for example because of a defect in the power control element, switches off the drive power source (for example, by interrupting fuel delivery, or the ignition in the case of positive-ignition internal combustion engines).
The above has been a brief discussion of certain deficiencies in the prior art and advantages of the invention. Other advantages will be appreciated from the detailed discussion of the preferred embodiment which follows.